1. Field of the Invention
The present invention relate to a method of assembling an electronic part device such as an LSI (large-scale integrated circuit) according to a face down method.
2. Description of the Prior Art
A flip chip method is one of the methods of assembling a semiconductor device made of a material such as Si and GaAs onto a circuit board. In this method, a semiconductor device where a bump is formed is assembled onto a circuit board according to a face down method.
FIG. 1, which shows a prior art, is a cross-sectional view showing a condition where a semiconductor device 10 is assembled onto a circuit board 11.
In the figure, the numerals 12 are bumps made of solder or gold and formed on the semiconductor 10. The bumps 12 are connected to conductive patterns 13 consisting of an ITO (indium tin oxide) film formed on the circuit board 11. The numeral 14 is a thermosetting resin sheet for fixing the semiconductor device 10 to the circuit board 11. The thermosetting resin sheet 14 hardens by being heated so that the volume thereof shrinks. Thereby, the semiconductor device 10 is fixed to the circuit board 11.
The process of the above-mentioned assembling method is as follows: first, the thermosetting resin sheet 14 with a thickness of approximately 25 .mu.m is bonded onto the circuit board 11; then, the semiconductor device 10 is arranged with its face down while the bumps 12 and the conductive patterns 13 formed on the circuit board 11 are positioned; and thereafter, the thermosetting resin sheet 14 is hardened while a condition is being maintained where the bumps 12 and the conductive patterns 13 are pressurized by a heating and pressurizing apparatus.
In a case where the bumps 12 formed on the semiconductor device 10 and the conductive patterns 13 formed on the circuit board 11 are pressed against each other by utilizing volume shrinkage force generated when the thermosetting resin sheet 14 is hardened as described above, the condition where the bumps 12 and the conductive patterns 13 are pressed against each other is maintained only by the thermosetting resin sheet 14 which is usually arranged in the center of the semiconductor device 10.
However, when the number of bumps is increased compared to an area where the thermosetting resin sheet 14 is bonded, the shrinkage force of the resin which acts on one bump decreases, so that an excellent pressing condition of the bumps 12 and the conductive patterns 13 cannot be maintained. Thereby, mal-assembling can occur.